The in vivo presentation and/or delivery of a biologically active agent within the body of a patient is common in the practice of modern medicine. In vivo presentation and/or delivery of biologically active agents is often implemented using medical devices that may be temporarily or permanently placed at a target site within the body. These medical devices can be maintained, as required, at their target sites for short or prolonged periods of time, in order to present and/or deliver biologically active agent at the target site.
For example, numerous polymer-based medical devices have been developed for the delivery of therapeutic agents to the body. Examples include drug eluting coronary stents which are commercially available from Boston Scientific Corp. (TAXUS), Johnson & Johnson (CYPHER), and others. In accordance with some typical delivery strategies, a therapeutic agent is provided within or beneath a biostable or biodegradable polymeric layer that is associated with a medical device. Once the medical device is placed at the desired location within a patient, the therapeutic agent is released from the medical device at a rate that is dependent, for example, upon the loading of the therapeutic agent and upon the nature of the polymeric layer.
For example, controlling the rate of therapeutic agent release and the overall dose are key parameters for proper treatment in many cases. Selection of the polymeric layer will have a great impact on these parameters. In many formulations, the thickness of the layer can be changed to control the total dose. However, control of the amount of therapeutic agent released in a specific time interval (e.g., the rate of release) presents greater challenges. The rate of release is generally a function of the material properties of the polymeric layer. Moreover, in many instances, the therapeutic agent becomes trapped in the release layer, never to be released.
It is also known that porous surfaces, including nanoporous surfaces can directly interact with cell receptors, thereby controlling the adhesion or non-adhesion of cells to the surface.